Generally, in a linear compressor, a compression space into/from which an operation gas is sucked and discharged is defined between a piston and a cylinder, and the piston is reciprocated linearly inside the cylinder to compress the refrigerant.
As the linear compressor includes a component for converting a rotation force of a driving motor into a linear reciprocation force of the piston, such as a crank shaft, a large mechanical loss is caused by the motion conversion. Recently, researches have been made to solve the above problem.
In the linear compressor, a piston is coupled directly to a linearly-reciprocating linear motor, so that a mechanical loss caused by the motion conversion is prevented. Therefore, the linear compressor can improve the compression efficiency and simplify the configuration. In addition, power inputted to the linear motor is regulated to control an operation of the linear motor, so that noise is less generated than in the other compressors. Accordingly, the linear compressor has been mostly used in an electric home appliance installed in an indoor space, such as a refrigerator.
FIG. 1 is a view illustrating one example of a conventional linear compressor, FIG. 2 is a view illustrating major portions of the one example of the conventional linear compressor, FIG. 3 is a graph showing a current supplied to a linear motor of FIG. 2, and FIG. 4 is a view illustrating the polar arrangement of the linear motor of FIG. 2.
Referring to FIGS. 1 and 2, in the one example of the conventional linear compressor, a structure composed of a frame 1, a stationary member 2, a moving member 3, a suction valve 4, a discharge valve assembly 5, a muffler assembly 6, a motor cover 7, a supporter 8, a main body cover 9, a buffering spring (not shown) and a linear motor 10 is installed inside a shell (not shown) to be elastically supported.
In detail, the stationary member 2 is formed in a hollow shape with both open ends. One end of the stationary member 2 is fitted into and fixed to the frame 1, and blocked by the discharge valve assembly 5. The discharge valve assembly 5 includes a discharge valve 5a, a discharge cap 5b and a discharge valve spring 5c. After vibration and noise of refrigerant discharged from the discharge cap 5b are reduced through a loop pipe (not shown), the refrigerant is discharged to the outside through an outflow tube (not shown) on the shell side.
The moving member 3 is formed in a hollow shape with one blocked end. The blocked end of the moving member 3 is inserted into the stationary member 2. A compression space P is defined between the stationary member 2 and the moving member 3. A plurality of suction holes 3a are formed in the blocked end of the moving member 3 so that refrigerant can be sucked into the compression space P therethrough.
The suction valve 4 is fixed to the blocked end of the moving member 3 to open and close the suction holes 3a of the moving member 3 according to pressure variations of the compression space P.
The muffler assembly 6 is formed at one open end of the moving member 3 to be elongated in a motion direction, and partitioned off into various spaces. Therefore, as refrigerant flows through each space, a pressure and a flow rate of the refrigerant are changed to reduce noise.
The motor cover 7 supports the linear motor 10 in an axis direction to fix the linear motor 10, and is bolt-fixed to the frame 1. The main body cover 9 is coupled to the motor cover 7 in an axis direction.
A predetermined suction hole is formed in the main body cover 9 so that refrigerant introduced from an inflow tube on the shell side can pass therethrough.
The supporter 8 is installed between the motor cover 7 and the main body cover 9 coupled thereto. The supporter 8 is fixed to the open end of the moving member 3. While the moving member 3 reciprocates linearly, the supporter 8 is elastically supported in an axis direction on the motor cover 7 and the main body cover 9 by the buffering springs.
Referring to FIG. 2, the linear motor 10 includes a cylindrical inner stator 11 fixed to the outside of the stationary member 2, an outer stator 12 disposed in a radius direction at a predetermined interval, and having one end supported on the frame 1 and the other end supported on the motor cover 7, a permanent magnet 13 installed between the inner stator 11 and the outer stator 12 with a predetermined gap, and a connection member 14 for connecting the moving member 3 to the permanent magnet 13.
While the inner stator 11 is formed by stacking laminations in a circumference direction, the outer stator 12 is formed by interlocking core blocks 12a and 12a′ on an outer circumferential surface of a coil wincing 12b wound in a circumference direction at a predetermined interval, and fixing the core blocks 12a and 12a′ to the coil wincing 12b by an insert-injected matter 12c. 
The operation of the conventional linear compressor will be described.
When input power is applied to the linear motor 10, as shown in FIG. 3, a current flows in the coil wincing 12b of the outer stator 12 with an AC waveform, and a flux alternates in +/− directions. Here, the inner stator 11, the outer stator 12 and the permanent magnet 13 generate a mutual electromagnetic force.
Referring to FIG. 4, the inner stator 11 and the outer stator 12 are repeatedly magnetized as N-S or S-N poles around the permanent magnet 13. The attractive and repulsive forces are operated between the poles (N-S) of the permanent magnet 13 and the magnetized poles of the inner stator 11 and the outer stator 12, so that the permanent magnet 13 reciprocates linearly.
Therefore, when the permanent magnet 13, the moving member 3 connected thereto, and the muffler assembly 6 reciprocate linearly, a pressure inside the compression space P is varied, so that the operations of the suction valve 4 and the discharge valve assembly 5 are automatically controlled. During the above operation, the refrigerant is sucked into the compression space P via the inflow tube on the shell side, the opening portion of the main body cover 9, the muffler assembly 6 and the suction holes 3a of the moving member 3, compressed in the compression space P, and discharged to the outside through the discharge cap 5b, the loop pipe and the outflow tube on the shell side.
In the conventional linear compressor, the coil wincing is installed inside the core blocks of the outer stator. When a current flows in the coil wincing, a flux is generated at an inner portion of the outer stator, i.e., around the coil wincing the to a mutual electromagnetic force. The flux flows through the frame made of steel, the stationary member, the moving member and the inner stator. Here, an iron loss occurs in sane of the flux flowing through the frame, the stationary member and the moving member, so that the efficiency of the linear motor is degraded.
In order to solve the foregoing problem, the frame, the stationary member and the moving member may be made of a non-magnetic material intercepting the flow of the flux. However, this method results in high cost and low productivity.